The present invention relates to a method of setting the reference data of shading corrections, and an image reading apparatus.
Heretofore, in an image reading apparatus, shading corrections have been implemented for output signals delivered as to individual photosensor elements mounted on an image sensor.
In implementing the shading corrections, reference data called “black reference data” and “white reference data” are employed. Before the image reading apparatus performs the operation of reading a subject such as photographic film, photograph, or printed document, it sets the black reference data and the white reference data by inputting a white reference image and a black reference image and then inspecting the output signals of the image sensor.
FIG. 4 is a diagram showing the relationship between the flow of a related-art process for reading a subject by setting white reference data and black reference data and a luminous intensity on that occasion. As shown in FIG. 4, in the related art, the black reference data are first set, and the white reference data are thereafter set. In the setting of the black reference data, there are performed the processing (step S205) of inputting a black reference image to an image sensor with a light source extinguished (point a in FIG. 4), and the processing (step S210) of setting the black reference data every photosensor element by inspecting the output signals of an image sensor as to the inputted black reference image. At a stage (point b in FIG. 4) when the processing of inputting the black reference image has ended, the light source is lit up. The luminous intensity of the light source lit up increases to a certain value monotonously with the lapse of time and is stabilized (point c in FIG. 4). When the setting of the black reference data has ended, and besides, the luminous intensity has been stabilized, the white reference data are subsequently set (step S220). In the setting of the white reference data, there are performed the processing of inputting a white reference image to the image sensor in a state where the light source is lit up, and the processing of setting the white reference data every photosensor element by inspecting the output signals of the image sensor as to the inputted white reference image. After the setting of the white reference data has ended, the processing of inputting the optical image of a subject to the image sensor and outputting image data outputted to shading corrections with the white reference data and the black reference data is started (step S225) in the state where the light source is lit up.
Since the errors of the white reference data exert serious influence on an image quality, the setting of the white reference data (step S220) is started after a sufficient wait since the lighting-up of the light source till the stabilization of the luminous intensity.
In general, the light source requires a time period of several seconds to dozens seconds since the lighting-up till the stabilization of the luminous intensity. Therefore, a long time is involved since the light source is lit up upon the end of the processing of inputting the black reference image, until the setting of the white reference data is started. This results in the problem that a time period before the start of the reading of the subject becomes long.